Many vehicles today are equipped with a cruise control to make it easier for the driver to drive the vehicle. The desired speed can then be set by the driver, e.g. via a control device in the steering wheel console, and a cruise control system in the vehicle acts thereafter upon a control system so that it accelerates and brakes the vehicle in order to maintain a desired speed. If the vehicle is equipped with an automatic gear change system, the vehicle's gears are changed so that the vehicle can maintain the desired speed.
When a cruise control is used in hilly terrain, the cruise control system will try to maintain a set speed on upgrades. This results inter alia in the vehicle accelerating over the crest of a hill and possibly into a subsequent downgrade, making it necessary to brake to avoid exceeding the set speed, which is a fuel-expensive way of running the vehicle.
By varying the vehicle's speed in hilly terrain it is possible to save fuel as compared with a conventional cruise control. This may be done in various ways, e.g. by calculations of the vehicle's current state (as with Scania Ecocruise®). If an upgrade is calculated, the system then accelerates the vehicle uphill. Towards the end of the climb, the system is programmed to avoid acceleration until the gradient has levelled out at the top, provided that the vehicle's speed does not drop below a certain level. Lowering the speed at the end of an upgrade makes it possible to regain speed on a subsequent downgrade without using the engine to accelerate. When the vehicle approaches the bottom of a dip, the system endeavours to use kinetic energy to embark on the next upgrade at a higher speed than an ordinary cruise control. The system will easily provide acceleration at the end of the downgrade in order to maintain the vehicle's momentum. In undulating terrain, this means that the vehicle starts the next climb at a higher speed than normal. Avoiding unnecessary acceleration and using the vehicle's kinetic energy makes it possible to save fuel.
If the topology ahead is made known by the vehicle having map data and GPS, such a system can be made more robust and can also change the vehicle's speed in anticipation.
There are existing systems which incorporate the topology ahead in the calculations for the vehicle's speed by doing real-time optimisations of the vehicle's speed across an itinerary. This may result in a very heavy computation load on the hardware in a real-time system in a vehicle, since such systems often have limited resources in terms of memory and processor power. Even doing ordinary calculations and simulations on line across the known route profile may represent a heavy computation load. If for example the precision or resolution of the horizon vectors for calculating road gradients is too great, unnecessary computation power is also involved.
A way of sparing the vehicle's computation power is referred to in published patent application US 2008/0188996 which refers to a driver assistance system in which a number of sensors supply attendant traffic factors and create hypotheses which are logically related to one another. However, that system is not related to cruise control of vehicles.
Published patent application US 2003/0163226 refers to a system for dynamic estimation of a vehicle's speed. Computation power can be saved by using an observer (LVP, linear parameter varying).
The object of the present invention is to propose an improved system for determining set-point values for a control system in a vehicle which in particular reduces the amount of computation power needed when set-point values for the vehicle's control systems have to be regulated.